OSPF Working Group X. Xu
Internet-Draft Alibaba Inc
Intended status: Standards Track S. Kini
Expires: November 14, 2019
P. Psenak
C. Filsfils
Cisco
S. Litkowski
Orange
May 13, 2019
Signaling Entropy Label Capability and Entropy Readable Label-stack
Depth Using OSPF
draft-ietf-ospf-mpls-elc-08
Abstract
Multiprotocol Label Switching (MPLS) has defined a mechanism to load
balance traffic flows using Entropy Labels (EL). An ingress Label
Switching Router (LSR) cannot insert ELs for packets going into a
given tunnel unless an egress LSR has indicated via signaling that it
has the capability of processing ELs, referred to as Entropy Label
Capability (ELC), on that tunnel. In addition, it would be useful
for ingress LSRs to know each LSR's capability of reading the maximum
label stack depth and performing EL-based load-balancing, referred to
as Entropy Readable Label Depth (ERLD), in the cases where stacked
LSPs are used. This document defines a mechanisms to signal these
two capabilities using OSPF and OSPFv3. These mechanisms are
particularly useful in the environment where Segment Routing (SR) is
used, where label advertisements are done via protocols like OSPF and
OSPFv3.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on November 14, 2019.
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Advertising ELC Using OSPF . . . . . . . . . . . . . . . . . 3
3.1. Advertising ELC Using OSPFv2 . . . . . . . . . . . . . . 4
3.2. Advertising ELC Using OSPFv3 . . . . . . . . . . . . . . 4
4. Advertising ERLD Using OSPF . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
[RFC6790] describes a method to load balance Multiprotocol Label
Switching (MPLS) traffic flows using Entropy Labels (EL). It also
introduces the concept of Entropy Label Capability (ELC) and defines
the signalings of this capability via MPLS signaling protocols.
Recently, mechanisms are being defined to signal labels via link-
state Interior Gateway Protocols (IGP) such as OSPF
[I-D.ietf-ospf-segment-routing-extensions]. In such scenario, the
signaling mechanisms defined in [RFC6790] are inadequate. This draft
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defines a mechanism to signal the ELC using OSPF. This mechanism is
useful when the label advertisement is also done via OSPF.
In addition, in the cases where stacked LSPs are used for whatever
reasons (e.g., SR-MPLS [I-D.ietf-spring-segment-routing-mpls]), it
would be useful for ingress LSRs to know each intermediate LSR's
capability of reading the maximum label stack depth and performing
EL-based load-balancing. This capability, referred to as Entropy
Readable Label Depth (ERLD) as defined in
[I-D.ietf-mpls-spring-entropy-label] may be used by ingress LSRs to
determine whether it's necessary to insert an EL for a given LSP of
the stacked LSP tunnel in the case where there has already been at
least one EL in the label stack [I-D.ietf-mpls-spring-entropy-label].
2. Terminology
This memo makes use of the terms defined in [RFC6790] and [RFC7770].
3. Advertising ELC Using OSPF
Even though ELC is a property of the node, in some cases it is
advantageous to associate and advertise the ELC with the prefix. In
multi-area network, routers may not know the identity of the prefix
originator in the remote area, or may not know the capabilities of
such originator. Similarly in the multi domain network, the identity
of the prefix originator and its capabilities may not be known to the
ingress LSR.
If a router has multiple line cards, the router MUST NOT announce ELC
unless all of its linecards are capable of processing ELs.
If the router support ELs on all of its line cards, it SHOULD
advertise the ELC with every local host prefix it advertises in OSPF.
When an OSPF Area Border Router (ABR) advertises the prefix to the
connected area based on the intra-area or inter-area prefix that is
reachable in some other area, it MUST preserve the ELC signalling for
such prefix.
When an OSPF Autonomous System Boundary Router (ASBR) redistributes
the prefix from other instance of the OSPF or from some other
protocol, it SHOULD preserve the ELC signalling for the prefix.
Exact mechanism on how to exchange ELC between protocol instances on
the ASBR is outside of the scope of this document and is
implementation specific.
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3.1. Advertising ELC Using OSPFv2
[RFC7684] defines the OSPFv2 Extended Prefix TLV to advertise
additional attributes associated with the prefix. The OSPFv2
Extended Prefix TLV includes a one octet Flags field. A new bit in
the Flags field is used to signal the ELC for the prefix:
0x20 - E-Flag (ELC Flag): Set by the advertising router to
indicate that the prefix originator is capable of processing ELs
3.2. Advertising ELC Using OSPFv3
[RFC5340] defines the OSPFv3 PrefixOptions that is advertised along
with the prefix. A new bit in the OSPFV3 PrefixOptions is used to
signal the ELC for the prefix:
0x04 - E-Flag (ELC Flag): Set by the advertising router to
indicate that the prefix originator is capable of processing ELs
4. Advertising ERLD Using OSPF
A new MSD-type of the Node MSD sub-TLV
[I-D.ietf-isis-segment-routing-msd], called ERLD is defined to
advertise the ERLD of a given router. The scope of the advertisement
depends on the application.
Assignment of a MSD-Type for ERLD is defined in
[I-D.ietf-isis-mpls-elc].
If a router has multiple linecards with different capabilities of
reading the maximum label stack deepth, the router MUST advertise the
smallest one.
5. Acknowledgements
The authors would like to thank Yimin Shen, George Swallow, Acee
Lindem, Les Ginsberg, Ketan Talaulikar, Jeff Tantsura , Bruno
Decraene and Carlos Pignataro for their valuable comments.
6. IANA Considerations
This document requests IANA to allocate one bit from the OSPFv2
Extended Prefix TLV Flags registry:
0x20 - E-Flag (ELC Flag)
This document requests IANA to allocate one bit from the OSPFv3
Prefix Options registry:
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0x04 - E-Flag (ELC Flag)
7. Security Considerations
The security considerations as described in [RFC7770] is applicable
to this document. This document does not introduce any new security
risk.
8. References
8.1. Normative References
[I-D.ietf-isis-mpls-elc]
Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
Litkowski, "Signaling Entropy Label Capability and Entropy
Readable Label Depth Using IS-IS", draft-ietf-isis-mpls-
elc-06 (work in progress), September 2018.
[I-D.ietf-isis-segment-routing-msd]
Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling MSD (Maximum SID Depth) using IS-IS", draft-
ietf-isis-segment-routing-msd-19 (work in progress),
October 2018.
[I-D.ietf-ospf-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", draft-ietf-ospf-segment-
routing-extensions-27 (work in progress), December 2018.
[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with MPLS
data plane", draft-ietf-spring-segment-routing-mpls-22
(work in progress), May 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
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[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>.
8.2. Informative References
[I-D.ietf-mpls-spring-entropy-label]
Kini, S., Kompella, K., Sivabalan, S., Litkowski, S.,
Shakir, R., and J. Tantsura, "Entropy label for SPRING
tunnels", draft-ietf-mpls-spring-entropy-label-12 (work in
progress), July 2018.
Authors' Addresses
Xiaohu Xu
Alibaba Inc
Email: xiaohu.xxh@alibaba-inc.com
Sriganesh Kini
Email: sriganeshkini@gmail.com
Peter Psenak
Cisco
Email: ppsenak@cisco.com
Clarence Filsfils
Cisco
Email: cfilsfil@cisco.com
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Stephane Litkowski
Orange
Email: stephane.litkowski@orange.com
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